In Radio Frequency (RF) systems, semiconductor packages for RF amplifiers or RF Integrated Circuits (ICs) are typically made by means of over-molding such that the dies and wires are covered by a mould compound. Examples of this art are the Quad Flat Non-leaded package (QFN), Heatsink Small Outline Package (HSOP) and Ball Grid Array (BGA) package styles.
Another typical concept for RF packages is an air cavity package. The function of the air cavity is to provide a dielectric with low dielectric relative permittivity e.g. close to 1.0 between the wire loops to create less electrical losses and enhance the performance of the RF product and system.
Air cavity packages are typically built-up by a stack of different materials, which encapsulate semiconductor dies, internal wiring and an air cavity as it is shown in FIG. 1.
For obtaining the structure according to the present application shown in FIG. 4 the so called dam and fill dispensing method is used. For obtaining a standard non-heat-degradable glob top it is necessary a high viscosity material to create a dam and a low viscosity material as encapsulant fluid to fill the “bath tub” within the dam perimeter. In the above method i.e. “dam and fill”, the dam is typically a rectangle of epoxy based fluid dispensed as lines or as a complete rectangle onto the substrate of the assembled package or assembled board for encapsulating the dies and the wires. The height of the dam can vary from slightly lower to slightly higher than the height of the parts within the dam perimeter. The width of the dam depends on the type of fluid and height.
The dam material typically needs fillers to increase viscosity. In the known art of “dam and fill” the epoxy based fluids contain fillers, such as silica.
FIG. 3a depicts a common process flow for an RF power amplifier package with air cavity.
FIG. 3b depicts a common process flow for an RF integrated circuit without air cavity.
The figures describing the above methods are self explanatory.
US-A 2007/0273013 provide systems and methods for producing micro electro-mechanical device packages. Briefly described, in architecture, one embodiment of the system, among others, includes a micro electro-mechanical device formed on a substrate layer; and a thermally decomposable sacrificial structure protecting at least a portion of the micro electro-mechanical device, where the sacrificial structure is formed on the substrate layer and surrounds a gas cavity enclosing an active surface of the micro electro-mechanical device. Other systems and methods are also provided.
Because of price erosion in RF products, it is a need for packages for RF products that are cheaper, especially the air cavity packages for RF products. A new package solution based on cheaper materials is needed for an air cavity package for RF products. Throughout the application we shall use the term the “encapsulant material” with the meaning of “the standard (epoxy) mold compound”.